Low-thrust lunar capture leveraging nonlinear orbit control

Nonlinear orbit control with the use of low-thrust propulsion is proposed as an effective strategy for autonomous guidance of a space vehicle directed toward the Moon. Orbital motion is described in an ephemeris model, with the inclusion of the most relevant perturbations. Unfavorable initial conditions, associated with weak, temporary lunar capture, are considered, as representative conditions that may be encountered in real mission scenarios. These may occur when the spacecraft is released in nonnominal flight conditions, which would naturally lead it to impact the Moon or escape the lunar gravitational attraction. To avoid this, low-thrust propulsion, in conjunction with nonlinear orbit control, is employed, to drive the space vehicle toward two different, prescribed, low-altitude lunar orbits. Nonlinear orbit control leads to identifying a saturated feedback law (for the low-thrust magnitude and direction) that is proven to enjoy global stability properties. The guidance strategy at hand is successfully tested on three different mission scenarios. Then, the capture region is identified, and includes a large set of initial conditions for which nonlinear orbit control with low-thrust propulsion is effective to achieve lunar capture and final orbit acquisition. For the purpose of achieving lunar capture, low-thrust propulsion is shown to be more effective if ignited at aposelenium

Low-thrust transfer to quasi-synchronous Martian elliptic orbit via nonlinear feedback control

This study considers the problem of injecting a spacecraft into an elliptic, repeating-ground-track orbit about Mars, starting from a 4-sol highly elliptical orbit, which is a typical Martian capture orbit, entered at the end of the interplanetary transfer. The final operational orbit has apoares corresponding to the maximum (or minimum) latitude, and nine nodal periods are flown in 5 Martian nodal days. The orbit at hand is proven to guarantee coverage properties similar to the Molniya orbit about Earth; therefore, it is especially suitable for satellites that form constellations. Low-thrust nonlinear orbit control is proposed as an affordable and effective option for orbit injection, capable of attaining significant propellant reduction if compared to alternative strategies based on chemical propulsion. This work introduces a new, saturated feedback law for the low-thrust direction and magnitude that is capable of driving the spacecraft of interest toward the operational orbit. Remarkable stability properties are proven to hold using the Lyapunov stability theory. Because no reference path is to be identified a priori, this technique represents a viable autonomous guidance strategy, even in the case of temporary unavailability of the low-thrust propulsion system or in the presence of widely dispersed initial conditions and errors on estimating orbit perturbations. Monte Carlo simulations prove that the feedback guidance strategy at hand is effective and accurate for injecting a spacecraft into the desired, repeating-ground-track operational orbit without requiring any reference transfer path

Mars Constellation Design and Low-Thrust Deployment Using Nonlinear Orbit Control

This research addresses the design of a Mars constellation composed of 12 satellites and devoted to telecommunications. While 3 satellites travel areostationary orbits, the remaining 9 satellites are placed in three distinct quasi-synchronous, inclined, circular orbits. The constellation at hand provides continuous global coverage, over the entire Martian surface. The use of 4 carrier vehicles, departing from a 4-sol orbit, is proposed as an affordable option for the purpose of deploying the entire constellation, even starting from dispersed initial conditions. Each carrier is driven toward the respective operational orbit using steerable and throttleable low-thrust propulsion, in conjunction with nonlinear orbit control. Lyapunov stability analysis leads to defining a feedback law that enjoys quasi-global stability properties. Orbit phasing concludes the constellation deployment, and is carried out by each satellite. The tradeoff between phasing time and propellant expenditure is characterized

Accesso alla giustizia dell'individuo nel diritto internazionale e dell'Unione europea

Questo libro si rivolge all'inquadramento della dinamica evolutiva del diritto internazionale rispetto al diritto dell'individuo all'accesso alla giustizia. La sua ampia articolazione su sei grandi tematiche - il diritto internazionale generale, i diritti umani, l'applicazione del principio di accesso alla giustizia nel diritto interno, la sua rilevanza nell'esecuzione di obblighi internazionali e della Carta delle Nazioni Unite, il diritto dell'Unione europea, le Commissioni di verità e riconciliazione - e la presa in considerazione delle più recenti manifestazioni della prassi internazionale, offrono una vasta panoramica che i curatori si augurano possa contribuire allo sviluppo della dottrina internazionale